"The Post decided not to report on the episode at the time because the flag-raising appeared to be the work of Martha-Ann Alito, rather than the justice, and connected to a dispute with her neighbors, a Post spokeswoman said."
So the answer to the question of why we're only just now hearing about this latest Supreme Court ethical violation 3 years later is that the Washington Post decided there was no story. "Democracy dies in darkness" indeed.
https://www.washingtonpost.com/politics/2024/05/25/alito-flag-martha-ann-washington-post/
The Washington Post · Wife of Justice Alito called upside-down flag ‘signal of distress’